A magnetic disk drive storage device typically comprises one or more thin film magnetic disks, each having at least one data recording surface including a plurality of concentric tracks of magnetically stored data, a spindle motor and spindle motor controller for supporting and rotating the disk(s) at a selected RPM, at least one read/write transducer or “head” per recording surface formed on a slider for reading information from and writing information to the recording surface, a data channel for processing the data read/written, a positionable actuator assembly for supporting the transducer in close proximity to a desired data track, and a servo system for controlling movement of the actuator assembly to position the transducer(s) over the desired track(s).
Each slider is attached on one surface to an actuator arm via a flexible suspension and includes on an opposite side an air bearing surface (ABS) of a desired configuration to provide favorable fly height characteristics. As the disk rotates, an air flow enters the slider's leading edge and flows in the direction of its trailing edge. The air flow generates a positive pressure on the ABS, lifting the slider above the recording surface. The slider is maintained at a nominal fly height over the recording surface by a cushion of air.
As recording density and data transfer rate have increased over the past a few years, critical dimensions in the recording device such as track width read and write gap and coil size have decreased accordingly. Also, the fly height between the air bearing surface (ABS) and the media has become smaller and smaller. For reference, recording heads with 40 gb/in2 products typically have fly heights of about 12 nanometers. Modern heads have even lower fly heights, and fly heights are expected to continue to decrease. This reduction in head critical dimensions and fly height, while beneficial to magnetic performance, also comes with cost on thermal and mechanic reliability. Particularly, with lower fly heights between the head and the magnetic disk during operation of the disk drive, there is an increasing rate of intermittent contacts between the head and the disk resulting in damage to the disk surface and wear on the head elements.
To help avoid the problems caused by intermittent head-disk contact, disks are lubricated during drive build. Although the disk is coated with lubricant during manufacture to protect it from such intermittent contact, during operation of the drive, the lubricant is eventually depleted from the surface of the disk. Because of the problems associated with lubricant spin-off from the disk, a vapor phase lubricant reservoir system has been disclosed as a means for continuously maintaining a uniform lubricant film on the disk. However, as fly heights are reduced, the slider will tend to contact the disk surface and, consequently, the lubricant. It has been observed that interaction between the slider trailing edge and the free lubricant can lead to severe instabilities, causing the slider to oscillate at its second pitch natural frequency (around 300 kHz for currently tested sliders) with an amplitude of more then 5 nm. This is a serious problem for reliability purposes. Thus it would be desirable to reduce lubricant induced slider oscillation by improving and stabilizing the clearance between the slider and the disk surface to reduce significant lubricant transfer between the disk and the slider.
Disk roughness also becomes more of a problem at lower slider flying heights.
With maximum peaks more likely to protrude into a normal range of slider operation, the probability of unintended and damaging slider/disk contact increases. The risk of damage from these discontinuities is greater at lower slider flying heights. Because of this, disks are being manufactured to have very smooth surfaces. Modern disks have a surface roughness (standard deviation Rq) of about 2–4 Å as measured in the 10–100 μm range along the disk surface, and typically have a microwaviness (standard deviation Wq) of 5 Å or more in the 100–1000 μm range.
The inventors have found that such smooth surfaces create another problem, that of stiction of the slider on the disk surface. Stiction is the tendency of smooth surfaces to stick together. As the disk rotates, stiction effects during slider-disk contact causes the slider to bounce, resulting in read and write instability. The inventors have found that stiction problems are more prevalent when using disks with low Rq and low Wq.
What is therefore needed is a way to enable reduced fly height while avoiding the hereinabove mentioned problems.